Angular adjustment mechanism, surgical alignment guide and surgical instrument assembly

ABSTRACT

An angular adjustment mechanism for a surgical instrument is described. The mechanism comprises an adjustment member ( 102 ) configured for rotation about a longitudinal axis ( 122 ), the adjustment member comprising a plurality of pairs of facets ( 134 ) arranged about the longitudinal axis. Each of the plurality of pairs of facets defines a respective angled axis ( 148 B, 148 C) at an angle ( 150 B, 150 C) relative to the longitudinal axis. A pivoting member ( 104 ) is arranged to pivot about a pivot axis perpendicular to the longitudinal axis and comprises a recess ( 128 ) for receiving the adjustment member and engaging one pair of the plurality of pairs of facets. This provides an angular adjustment mechanism in which facets on the outside of the adjustment member engage corresponding surfaces in a recess on a pivoting member. The use of facets provides a secure connection while allowing a greater degree of angular adjustment and providing a further benefit of simple operation.

CROSS REFERENCE TO RELATED APPLICATION

This application is a National Stage 35 U.S.C. 371 of InternationalPatent Application PCT/GB2011/052173, filed Nov. 8, 2011.

BACKGROUND OF THE INVENTION

The present invention relates to an angular adjustment mechanism,surgical alignment guide and surgical instrument assembly. The presentinvention is particularly applied to orthopaedic surgery and especiallyknee surgery.

In orthopaedic knee surgery, a cut may be made to the femoral head inorder to correct varus or valvus alignment. A cutting guide is used tolocate the cut accurately. A cutting guide is fixed to the bone usingpins and provides a stable surface to guide resection of the femoralhead.

In order to ensure the cutting guide is placed correctly on the femur,an alignment system is typically used. An intramedullary rod is insertedinto the intermedullary canal of the femur, providing a stable referenceto the intramedullary axis of the femur. An alignment guide is disposedon this rod. The alignment guide contains a scale indicating the desiredangle of the cut relative to the intramedullary axis of the femur and anangular adjustment mechanism. The cutting guide is attached to thealignment guide and advanced along the rod until it is in contact withthe femur. It is aligned at the desired angle by the alignment guide. Itcan then be secured in place.

WO-A-2009/037471 describes an example of such an alignment guide. Theinstrument comprises an angular adjustment mechanism which includes anadjustment member which is rotatable about the longitudinal axis of anintramedullary rod. The adjustment member has an end surface defining aplurality of slots located between recesses or notches, giving the endof the adjustment member a castellated appearance. Each slot defines adifferent angle relative to the longitudinal axis. A selected slotengages a rib formed on a pivoting member, thereby rotating the pivotingmember to a desired angle.

The mechanism of WO-A-2009/037471 has disadvantages because the spaceavailable for the adjustment member limits its size. The size sets alimit on the number of different slots the adjustment member can defineto ensure that the pivoting member is held securely. In practice, therecess needs to be of a minimum width to engage the ridge firmly. Thewalls defining the recess also need to have a minimum size to preventtheir deformation or failure. The limit on the number of slots limitsthe range of adjustment possible. For example, WO-A-2009/037471discusses an embodiment in which the angular adjustment is in incrementsof 2 degrees or greater, for example, different slots define 3, 5 or 7degrees of angular adjustment. It would be desirable to provide analignment guide in which the angular adjustment mechanism can providefiner degrees of angular adjustment.

Accordingly, the present invention provides an angular adjustmentmechanism in which facets on the outside of the adjustment member engagecorresponding surfaces in a recess on a pivoting member. The use offacets allows a secure connection to be achieved without requiringintermediate walls or edges as are required using a slot on the angularadjustment member as taught by WO-A-2009/037471 (because the walls arenecessary to define the recess). This allows a greater degree of angularadjustment and a further benefit of simpler operation.

According to a first aspect of the present invention there is providedan angular adjustment mechanism for a surgical instrument comprising anadjustment member configured for rotation about a longitudinal axis, theadjustment member comprising a plurality of pairs of facets arrangedabout the longitudinal axis; wherein each of the plurality of pairs offacets defines a respective angled axis at an angle relative to thelongitudinal axis; and a pivoting member arranged to pivot about a pivotaxis perpendicular to the longitudinal axis and comprising a recess forreceiving the adjustment member and engaging one pair of the pluralityof pairs of facets.

BRIEF SUMMARY OF THE INVENTION

Each pair of facets may be mutually opposed about the longitudinal axis.The plurality of pairs of facets may extend completely around thelongitudinal axis or only partially around the longitudinal axis.

The pivot axis preferably intersects the longitudinal axis forsimplicity of construction, however, this is not essential and it couldbe located elsewhere in some embodiments, for example, by using alinkage.

Each of the plurality of pairs of facets may define a respective angledaxis which is at a different angle relative to the longitudinal axisthan others of the plurality of pairs of facets, although in someembodiments there may be duplication of the angled axis betweendifferent pairs of facets, depending on the application.

The adjustment member is preferably translatable along the longitudinalaxis to allow it to disengage and engage the recess. However, otherarrangements are possible, for example, manufacturing one or both of thefacets and/or the recess from a resilient material, enabling deformationto allow rotation of the adjustment member in situ within the recess.

In use, the respective angled axis defined by each pair of facets allowsthe angle of the pivoting member to be set by rotation of the adjustmentmember. For example, in one embodiment the facets may be provided with aregular difference between each angled axis, for example each pair offacets may differ from an immediately adjacent pair in one degree steps,two degree steps or any other amount as appropriate. One embodimentcomprises an odd number of pairs of facets. This enables one pair todefine a zero degree pivot and the other pairs to define the same rangeof positive and negative (clockwise or anticlockwise) rotation about thepivot axis.

An angular adjustment mechanism according to the invention can provide afiner degree of adjustment than the prior art. This is because thefacets engage the recess and they are defined by a surface of theadjustment member itself, no walls are needed as are required when arecess is used. A further benefit of the use of facets is easiercleaning and assembly.

Preferably, each respective angled axis is defined by rotating each ofthe plurality of pairs of facets about the same predetermined point onthe longitudinal axis. This simplifies construction by ensuring thatwhichever pair of facets is selected, the rotation is about the samepoint, without a need to provide an intermediate linkage mechanism.

In one embodiment, the pivot axis intersects the longitudinal axis andthe predetermined point on the longitudinal axis is where the pivot axisintersects the longitudinal axis. This enables the adjustment member todirectly alter the position of the pivoting member without requiring anintermediate linkage.

Each facet of the plurality of pairs of facets may be substantiallyplanar and the axis of rotation for each respective angled axis may thenbe parallel to the plane of the facets and perpendicular to thelongitudinal axis. This means that the axis of rotation is in a slightlydifferent direction for each pair of facets, it is not the same forevery pair of facets. The effect is that the axis of rotation rotatesaround the predetermined point depending on which pair of facets isselected. This rotation ensures that when a selected pair of facets areengaged in the recess the axis of rotation of those facets is alignedwith the pivot axis.

Preferably, each of the plurality of pairs of facets define a taper inthe direction of the angled axis. The taper means that the facetspresent a narrowing profile in the direction of the angled axis. Thisprovides a self-centering effect to ensure that the adjustment member issecurely located within the recess. It also simplifies engagement andrelease of the adjustment member as required while still ensuring asecure connection when the adjustment member is engaged in the recess.

Preferably, the taper angle is between ten degrees and thirty degrees.The reference to the taper angle refers to the angle formed between theplanes defined by each pair of facets if the planes are extended to thepoint where the two planes intersect. Preferably the taper angle isgreater than the range of angular adjustment between the respectiveangled axes. This is preferred to ensure that the taper is still presentno matter what the rotation of the angular adjustment member. Forexample, if a degree of angular adjustment of ±9° is required, the totaladjustment is 18° and a taper angle of 20° or more is preferred. Thisensures that even at the extreme adjustment of ±9° there is still aslight taper at both sides with respect to the longitudinal axis.

In one embodiment, each of the plurality of pairs of facets iscontiguous with another of the plurality of pairs of facets. Theplurality of pairs of facets then extend all the way around thelongitudinal axis.

At least a part of each edge between respective ones of the plurality offacets may then be cut away or scalloped. This cut away will extendpartially into the facet itself. The cut away portion enables easierrotation of the angular adjustment member to select an alternative pairof facets. Without the cut away, the edge between facets may snag on therecess. Including the cut away means that a smaller amount oftranslational movement of the adjustment member along the longitudinalaxis is required to disengage a pair of facets from the recesssufficiently to enable rotation to select a different pair of facets.

Preferably, each respective angled axis is defined by rotating each ofthe plurality of pairs of facets about the same predetermined point onthe longitudinal axis and the cut away portion of each edge extends forthe same distance from the predetermined point in the direction of therespective angled axis. Thus, when viewed along the longitudinal axis,the cut away portion extends different lengths on each side of theadjustment member, relative to the longitudinal axis. This ensures thatsufficient portion is cut away to enable the improved rotation of theadjustment member, but the length of cut away is minimised to improvethe surface area of the facet available to engage with the recess.

The recess may comprise a pair of mutually opposed projections forengaging one of the plurality of pairs of facets. Use of a projectionhas been found to provide a secure connection with the facet whileenabling easier adjustment of the angular adjustment member if required.Alternative embodiments may not use a projection and in that case thefacet may directly engage a side of the recess.

The angular adjustment mechanism may further comprise a resilient memberfor biassing the adjustment member into the recess of the pivot member.This helps to ensure a secure connection between the adjustment memberand the pivot member.

The angular adjustment mechanism described above may form part of asurgical alignment guide. The surgical alignment guide may be combinedwith a cutting guide attached to the pivot member to form a surgicalinstrument assembly. The cutting guide can be directly or indirectlyattached to the pivot member. If the cutting guide is indirectlyattached to the pivot member and intermediate portion may be connectedbetween the cutting guide and the pivot member.

The surgical instrument assembly may further comprise an intramedullaryrod defining an intramedullary axis. In that case the angular adjustmentmechanism is installed on the intramedullary rod and the longitudinalaxis of the adjustment member is coaxial with the intramedullary axis.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly with reference to the accompanying drawings, in which:

FIG. 1 depicts a perspective view of an alignment guide, cutting guideand intramedullary rod before connection of the cutting guide to thealignment guide;

FIG. 2 depicts a perspective view of an alignment guide, cutting guideand intramedullary rod as shown in FIG. 1, after the cutting guide hasbeen connected to the alignment guide.

FIG. 3 shows a plan view of the system of alignment guide, cutting guideand rod of FIG. 2;

FIG. 4 depicts a cross-section through the attachment protrusion andcorresponding recess when the alignment guide has been connected to thecutting guide;

FIGS. 5a-5e show cross-sections through the alignment guide and cuttingguide showing the disconnection of the alignment guide from the cuttingguide;

FIG. 6 depicts an intramedullary rod for use with the cutting guide andalignment guide of the system;

FIG. 7 depicts a perspective view of an alignment guide installed on theintramedullary rod of FIG. 6;

FIG. 8 depicts a cross-section through the intramedullary rod andalignment guide before the alignment guide is secured on theintramedullary rod;

FIG. 9 depicts a cross-section through the intramedullary rod andalignment guide after the alignment guide is secured on theintramedullary rod;

FIG. 10 depicts a cross-section showing a rotation limiting connectionbetween the alignment guide and the intramedullary rod;

FIG. 11 depicts a perspective view of an alternative alignment guide;

FIG. 12 depicts a cross section of the alignment guide of FIG. 11;

FIG. 13 depicts an exploded view of selected components of the alignmentguide of FIG. 11;

FIG. 14 depicts a perspective view of an adjustment member of thealignment guide of FIG. 13;

FIG. 15 depicts an end view of the adjustment member of FIG. 14;

FIGS. 16A-16C depict cross sections through the adjustment member ofFIG. 14;

FIG. 17 depicts a perspective view of a pivoting member of the alignmentguide of FIG. 13;

FIG. 18 depicts an exploded view of a cutting guide attachment part foruse with the alignment guide of FIG. 16; and

FIG. 19 depicts a perspective view of an alignment guide, cutting guideand intramedullary rod with the intramedullary rod inserted to theintramedullary canal of a femur.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts a perspective view showing components of a surgicalinstrument system for aligning a cutting guide. The system comprises anintramedullary rod which comprises a cylindrical member 2 havinglongitudinal grooves 4 formed along its length. In use the cylindricalsection 2 is inserted into the intramedullary canal of a femur and thelongitudinal grooves 4 provide means for pressure release duringinsertion.

An alignment guide 6 (shown partially in FIG. 1) comprises a throughbore into which the cylindrical section 2 of the intramedullary rod isinserted, so that the alignment guide 6 can move longitudinally alongthe cylindrical section 2 and also rotate relative to the cylindricalsection.

A cutting guide 8 is provided separately from the alignment guide 6. Thecutting guide 8 comprises a cutting slot 10 which defines the cut to bemade to the bone. Cutting guide 8 also comprises attachment holes 12 forfixing the cutting guide 8 to the bone. Cutting guide 8 is attached tothe alignment guide 6 by means of a recess 14 and an attachment surface16 on its upper surface. The recess 14 has a shape corresponding to anattachment protrusion 18 formed on the alignment guide 6.

Attachment protrusion 18 comprises a first cylindrical portion 20 havinga first diameter and a second cylindrical portion 22 having a seconddiameter which is larger than the first diameter. The first diameter isabout 4 mm and the second diameter is about 12 mm in this embodiment.Other dimensions may be used in other embodiments. The first and secondcylindrical portions 20, 22 share a common axis. Joining the firstcylindrical section to the second cylindrical section 22 is a generallyfrustoconical portion 24. The recess 14 defines surfaces correspondingto the first and second cylindrical portions 20, 22 of the attachmentprotrusion 18.

In use, when the attachment protrusion 18 is inserted into recess 14,first cylindrical portion 20 and second cylindrical portion 22 engagecorresponding surfaces within the recess so that the cutting guide 8 issecurely aligned with the longitudinal axis of the attachment protrusion18. The dimensions of the corresponding surfaces within the recess areclose to the dimensions of the first cylindrical portion 20 and thesecond cylindrical portion 22 but very slightly larger. This ensuresfirm connection but reduces the likelihood of a tight fit between theattachment protrusion 18 and the recess 14 making it difficult to removethe attachment protrusion 18 from the recess 14.

The cutting guide 8 is further secured in place on the attachmentprotrusion 18 of the alignment guide 6 by a clip member 26 on thealignment guide 6. The clip member 26 engages the attachment surface 16of the cutting guide 8. A perspective view of the cutting guide 8installed on the alignment guide 6 can be seen in FIG. 2.

FIG. 3 shows a plan view of the system of alignment guide 6, cuttingguide 8 and rod assembled together. FIG. 3 also depicts two adjustmentscales 28, 30 provided on the alignment guide 6. The two adjustmentscales 28, 30 allow the relative rotation of parts of the alignmentguide to be set as determined by a surgeon to alter the varus valgusrotation of the attachment protrusion 18 relative to the intramedullaryaxis defined by the cylindrical portion 2 of the rod and the throughbore in the alignment guide 6. The cutting guide 8 is installed on theattachment protrusion 18 and hence its alignment is altered relative tothe intramedullary axis.

FIG. 4 depicts a cross-section of the assembled system, taken throughthe connection recess. This shows how the cutting guide is secured onthe alignment guide by the engagement of cylindrical portions 20, 22 incorresponding sections of the recess. FIG. 4 also enables the internalconstruction of the connection recess 14 to be understood more clearly.The cross-section illustrates enlarged portion 32. Enlarged portion 32includes an initial section perpendicular to the longitudinal axis ofthe recess following a short tapered section 34 from the firstcylindrical section. Enlarged section 32 has a greatest dimensionperpendicular to the longitudinal axis which is larger than the diameterof the second cylindrical section. This provides a greater range ofmovement for the first cylindrical section 20 within the recess duringdisconnection of the alignment guide 6 from the cutting guide 8. Taperedsection 34, adjacent the first cylindrical section 36 of the cuttingguide 8 serves to guide the tip of the attachment protrusion 18 into thefirst cylindrical section 36.

The enlarged central section 32 extends perpendicular to thelongitudinal axis through the entire depth of the cutting guide. Thisallows the enlarged central section to also provide attachment surface16 for clip 26.

The second cylindrical section is formed in the portion of the cuttingguide adjacent cutting slot 10.

The disconnection of the cutting guide from the alignment guide will nowbe described. To illustrate the benefits of this system, the cuttingguide is depicted in FIG. 5a connected to the alignment guide 6 with thevarus valgus adjustment 28 of the alignment guide adjusted to a maximumin the right-hand direction. This shifts the angle of the longitudinalaxis of the attachment protrusion 18 and cutting guide 8 relative to thelongitudinal axis of the cylindrical section 2, and can clearly be seenin FIG. 5a . In prior art devices this configuration can be difficultfor a surgeon to disconnect the alignment guide from the cutting guide.The difference in angles between the anatomic axis (defined by thecylindrical section 2 of the rod) and the mechanical axis, in additionto the offset of the attachment protrusion with the alignment guide makeit difficult to remove cleanly. The alignment guide is constrained bythe cylindrical section 2 to move along the anatomical axis, notmechanical axis.

As shown in FIG. 5b , in the present system, after relatively littlemovement, for example as small as 1.5 mm, the first and secondcylindrical sections of the connection are disengaged. After a furthershort movement, the first cylindrical section of the attachmentprotrusion enters the enlarged section 32 of the recess in the cuttingguide. At this point, there is significant freedom of movement betweenthe attachment protrusion 18 of the alignment guide and the recess 14 ofthe cutting guide. As shown in FIG. 5d , the disconnection of thecylindrical sections enables simple removal of the attachment protrusionalong the anatomical axis defined by cylindrical section 2, withoutneeding complicated manipulation, until as shown in FIG. 5e theattachment protrusion 18 is well clear of the cutting guide. Thecylindrical section of the rod can then be withdrawn from theintramedullary canal, leaving the cutting guide in place.

Unlike prior art systems, the stepped nature of the attachmentprotrusion 18 and corresponding recess, including first and secondcylindrical portions with different diameters, enables disconnection ofan attachment protrusion to be achieved over much shorter distances.This gives greater freedom of movement between the parts, simplifyingseparation of the alignment guide from the cutting guide after thecutting guide is in place. This can allow a user more freedom in choiceof the technique used to disconnect the cutting guide and allow onehanded removal in certain circumstances.

The system is used with an intramedullary rod 40 which is illustrated inits entirety in FIG. 6. The intramedullary rod 40 comprises a handle 42,a cylindrical section 2 having grooves 4 formed therein (as describedabove) and a rounded end 44 at the distal end of the cylindrical section2, furthest from the handle 42. At a proximal end of the cylindricalsection 2, close to the handle 42, a protrusion 46 is provided whichextends circumferentially around the cylindrical section 2. Proximal ofthe protrusion 46, a second protrusion 48 is formed around thelongitudinal axis defined by the cylindrical section 2. As will bedescribed in more detail below, protrusion 46 and protrusion 48 formparts of a restraining system for retaining an alignment guide inposition on the intramedullary rod 40 while the rod 40 is being insertedor removed from an intramedullary canal.

The protrusion is 46 is about 65 mm from the proximal end of the handle42. This distance, and the length of the rod 40, may be varied dependingon the length of rod 40 required to extend beyond an alignment guide 6when engaged with the restraining system. For example, the rod 40 mayextend up to 300 mm. In use the rod 40 may not be inserted into anintramedullary canal to its full length. The depth of insertion may belimited, for example by a hip stem already present in the canal from anearlier hip replacement procedure. To allow for this, the alignmentguide 6 can be released from the restraining system and moved along therod 42 to engage the bone surface.

FIG. 7 depicts a perspective view of the proximal end of anintramedullary rod 40 with an alignment guide 6 mounted thereon. Across-section showing the way in which the alignment guide 6 is mountedon the intramedullary rod 40 is given in FIG. 8. FIG. 8 depicts how thealignment guide 6 comprises a through bore 50 which receives cylindricalsection 2 of the intramedullary rod 40. As depicted in FIG. 8, thealignment guide 6 can be moved freely along the longitudinal axisrelative to the rod and rotated relative to that axis. During insertionand removal of the intramedullary rod to the intramedullary canal, thefree movement of the alignment guide can mean that two hands arerequired, one to insert the rod and the other to ensure that thealignment guide does not move relative to the rod during insertion.

To secure the alignment guide relative to the rod, FIG. 9 shows howprotrusions 46, 48 engage corresponding features in the alignment guideto prevent longitudinal movement of the alignment guide along the rodand also to prevent rotation of the alignment guide relative to the rod.Ring shaped protrusion 46 on the intramedullary rod is formed from aresilient material. This engages a corresponding groove 52 in thethrough bore 50 of the alignment guide 6. The resilient nature of theprotrusion 46 means that it can be compressed by a small force beforeexpanding into the groove 52. This holds the alignment guide 6 securelyon the rod 40, preventing relative longitudinal movement.

In some embodiments, the protrusion 46 may be made of a material with ahigh coefficient of friction so that it can also prevent rotation of thealignment guide about the longitudinal axis as well as longitudinalmovement. However, a second protrusion 48 may also be provided toprevent rotation. Although not clear from the cross-section in FIG. 9,protrusion 48 has a polygonal shape centred on the longitudinal axis.This engages a corresponding recess 54 formed in the alignment guide.FIG. 10 shows the engagement between protrusion 48 and recess 54 moreclearly. Protrusion 48 has a generally octagonal shape centred on thelongitudinal axis. Together, the engagement of protrusion 48 with therecess 54 prevents rotation of the alignment guide 6 relative to the rod40 when the first protrusion 48 is engaged with groove 52.

Thus, the connection between the rod and the alignment guide can be madesecure during insertion or removal of the intramedullary rod. When it isdesired to use the alignment guide 6 to place the cutting guide 8 in thecorrect position, the alignment guide 6 is moved longitudinally in adistal direction to disengage both protrusion 48 from channel 54 andprotrusion 46 from groove 52. Alignment guide 6 is then free totranslate and rotate about longitudinal axis of the cylindrical section2.

FIG. 11 depicts a perspective view of an alignment guide 100 whichallows a fine degree of control over the angular adjustment. As shown inFIG. 11, the alignment guide comprises an adjustment member 102 and apivoting member 104. The adjustment member is disposed over alongitudinal shaft 106 which defines a longitudinal axis. Longitudinalshaft 106 is hollow, enabling the alignment guide to be installed on anintramedullary rod (not shown). The pivot member 104 is pivotallyattached to the shaft 106 by passing pins 108, 110 through openingsdefined in the pivot member 104 and engaging corresponding openings 112,114 formed in an end of the shaft 106.

An indicator member 116 is provided at the other end of the shaft to thepivotal connection. This includes a pointer 118 which extends over theend of the adjustment member 102 to overlap a visual indicia of thedegree of angular adjustment applied by the adjustment member 102.

The adjustment member 102 is shorter than the distance between the endof indicator member 116 and the pivot point 112, 114. This enablesadjustment member 102 to translate back and forth along the longitudinalaxis 122. A resilient member 120, which is a helical spring in thisembodiment, is disposed around the shaft 106. This provides a force topush the adjustment member 102 towards the pivot point 112, 114 in theabsence of an applied force.

The assembled alignment guide 100 is shown in cross-section in FIG. 12.This enables the relationship of the various components to thelongitudinal axis 122 to be seen clearly. FIG. 13 depicts an explodeddiagram showing the construction between the shaft 106, resilient member120 and adjustment member 102.

Adjustment member 102 includes an end portion which comprises aplurality of pairs of facets 134. Each pair of facets 134 is contiguouswith another pair of facets 134. The forward end of the edge betweeneach pair of facets comprises a cut away portion 138. The configurationof the facets 134 and cut away portions 138 will be described in moredetail below.

The pivoting member 104 comprises a recess 128 for receiving the endportion of the adjustment member. The recess 128 includes projections130. The projections 130 are positioned to engage one pair of facets 134when the end portion of the adjustment member 102 is located in therecess. In the absence of an applied force, the force provided byresilient member 120 ensures that a pair of facets 134 is engaged withthe projections 130 of the recess 128. The configuration of the recess128 and projections 130 can be seen more clearly in FIG. 17 which is aperspective view of the pivoting member from the opposite direction tothat shown in FIG. 11.

In use, the interaction between a pair of facets 134 on the adjustmentmember 102 with the projections 130 on the recess 128 acts to rotate thepivoting member about the axis defined by the pins 108, 110. Thispivoting is achieved by the specific arrangement of facets 134 providedon the adjustment member 102. The arrangement of these facets will nowbe described with reference to FIGS. 14, 15 and 16A-16C.

FIG. 14 depicts a perspective view of the adjustment member 102. Itshows how the adjustment member comprises a plurality of facets 134 atone end. Facets 134 are arranged in mutually opposed pairs about thelongitudinal axis. The configuration of each pair of facets 134 ischosen so that they define an axis which is angled with respect to thelongitudinal axis. FIG. 15 depicts an end view of the adjustment member102. It shows how the facets are evenly spaced at regular angularspacings around the longitudinal axis 122. In this embodiment, there arenineteen pairs of facets respectively defining angles of of 0° and ±9°.

FIG. 16A shows a cross-section along line A-A in FIG. 15. This pair offacets 134A defines an axis which is coincident with the longitudinalaxis 122, or at an angle of 0°. In this example, all of the pairs offacets 134 define a taper of 20°. Thus, both facets 134A are offset by10° from the longitudinal axis to define a taper of 20°. This angularadjustment is indicated by arrows 136A in FIG. 16A.

As discussed above, to facilitate rotation of the adjustment member 102when it is disengaged from the recess, cut outs 138 are provided at theend. Cut outs 138A depicted in FIG. 16A extend approximately 5.5 mm fromthe end of the adjustment member 102. This is indicated by referencenumeral 140A. The width of the adjustment member just before the cut outis approximately 25 mm, indicated by reference number 142A. Dimension144A is approximately 24 mm, showing the taper and dimension 136A isapproximately 3 mm. Other dimensions may be used in other embodimentsdepending on the particular requirements.

For an angle of 0°, i.e. an axis which is coincident with thelongitudinal axis FIG. 16A shows that the configuration of the endportion in cross-section at the pair of facets 134A is symmetrical.Thus, when pair of facets 134A engage the projections 130 the recess isrotated to be aligned with the longitudinal axis.

FIG. 16B depicts a cross-section along line B-B in FIG. 15. At thisposition, the pair of facets 134B together define an angled axis 148Bwith respect to the longitudinal axis 122. As indicated by angulardimension 150B, the angled axis 148B is 4° offset from longitudinal axis122. Angled axis 148B is defined by facets 134B which have been rotatedabout a point 152. Point 152 lies on the longitudinal axis 122approximately 5.5 mm from the top of the adjustment member 102, asindicated by distance 154. The taper of the facets 134B is the same asfor facets 134A, 20°. However, the taper is defined with reference tothe angled axis 148B. This means that when the facets 134B engage theprojections 130 the pivoting member will be pivoted through 4° becauseof the self-centering nature of the taper. Point 152 is chosen to becoincident with the axis of pins 108, 110.

When facets 134B are engaged with pivoting member, the pivoting memberis rotated relative to the longitudinal axis consistent with therotation of the facets 134B along angled axis 148B. Thus, the cut out138B extends a different distance either side of the adjustment member102 to ensure that they are the same distance from the pivot member,when facets 134B are engaged by projections 130. Dimension 156 isapproximately 11 mm from the pivot point 152. This 11 mm distance ismeasured in the direction of angled axis 148B. Thus, cut out 138B isshorter than cut out 138B′. Dimensions 142B, 144B and 146B correspond todimensions 142A, 144A and 146A for consistency with all embodiments.

To further assist the explanation, FIG. 16C depicts a cross-section ofthe adjustment member 102 taken along line CC in FIG. 15. Thiscorresponds to an adjustment of 9° as indicated by angle 150C in FIG.16C. The angling of angled axis 148C is more pronounced in thiscross-section. This means that the distance of cut outs 138C on theright hand side of the diagram is again shorter than the cut out 138C′on the left hand side. The length of the cut out is again determined byprojecting a line approximately 11 mm from the pivot point 152 andextending the cutout 138C, 138C′ in the direction of the angled axis148C distance 156 (approximately 11 mm in this embodiment). Theremaining dimensions 142C, 144C, 146C remain the same as 142A, 144B and146C.

FIG. 16C demonstrates how the facets 134C are still tapered with respectto the longitudinal axis 122. This is because the taper angle of 20°means that with the 9° relative angle of axis 148C there remains 1° oftaper depicted on the left hand side of FIG. 16C. This ensures that thetaper remains with respect to the longitudinal axis (although it is notsymmetrical about the longitudinal axis 122).

In use, the angle of the pivoting member is adjusted by withdrawing theadjustment member 102 proximally against the biassing force of resilientmember 120. This disengages the facets from the projections in thepivoting member 104. The adjustment member is then rotated until theindicator 118 points at the desired degree of angular adjustment. Thisis indicated by markings or indicia 160 on the adjustment member 102.The adjustment member can then be released and the action of theresilient member 120 pushes the end of the adjustment member into therecess 128 of the pivoting member. The pair of facets 134 correspondingto the desired angular adjustment as indicated by indicator 118 engageprojections 130. The taper ensures that the pivoting member is centredand securely located on the facets. Depending on the angle of the axisdefined by the pair of facets, the pivoting member is turned to thedesired angle by the engagement of the facets with the projection.

In this embodiment, a cutting guide is attached to the pivoting member104 by an intermediate translating assembly 162. Translating assembly162 comprises an attachment member 164 which includes a steppedconnection 166 and clip 168 for attaching a cutting guide (not shown)and a translation adjustment mechanism 170. Translation adjustmentmechanism 170 comprises an adjustment dial 172 which adjusts thetranslation of the cutting guide relative to the alignment guide byadjusting the degree to which shaft 174 is inserted into a correspondingrecess in translation adjustment guide 170. (The parts of this assemblyare shown in exploded form in FIG. 18 for clarity).

It will be appreciated that the configuration depicted in FIGS. 11-18differs in some minor aspects of appearance with configuration depictedin FIGS. 1-10 and 19. The features of angular adjustment and features ofthe adjustment member described in relation to FIGS. 11-18 can beapplied to FIGS. 1-10 and 19.

Where dimensions are described, they are for example only and are notlimiting. Alternative dimensions may be used in other embodiments.

FIG. 19 depicts a system of alignment guide, rod, handle and cuttingguide in use, inserted into a femur before the alignment guide isadvanced along the rod to engage the cutting guide with the femur.

The improved connection between a cutting guide and an alignment guidemay be used in other applications than for knee surgery, for example, itis applicable to any situation in which an alignment axis is not thesame as a guiding axis. The stepped principle could also be applied toany system in which disconnection with short longitudinal movement isrequired. The connection between the alignment guide and the rod may beused in any circumstance in which an alignment guide is used with a rod,not only those where an alignment guide is used to install a cuttingguide for knee surgery as described above. The improved angularadjustment mechanism may be used with any surgical instrument requiringangular adjustment, not only for use in knee surgery.

Although a system comprising an alignment guide, cutting guide and rodhas been described, the stepped attachment protrusion for connecting thecutting guide and alignment guide can be used in systems which do notinclude a rod. Likewise the restraining system between the alignmentguide and rod can be used in systems which do not include a cuttingguide. The stepped attachment system and the restraining system can beused with other alignment guides than the faceted guide described above,for example they may be used with the mechanism discussed inWO-A-2009/037471.

The elements of the above described system are constructed from medicalgrade materials. For example the rod may be manufactured from medicalgrade metal and the other components from medical grade plasticsmaterials or metals.

The invention claimed is:
 1. A surgical instrument assembly comprising:an adjustment member comprising a plurality of pairs of facets arrangedabout a longitudinal axis, each pair of facets meeting along an edge,the adjustment member being rotatable about the longitudinal axis;wherein each edge of the plurality of pairs of facets lies along a lineintersecting the longitudinal axis at an angle, each edge defining adifferent angle with respect to the longitudinal axis; a pivoting memberpivotable about a pivot axis that is perpendicular to the longitudinalaxis, the pivoting member having a recess sized to engage at least onepair of the plurality of pairs of facets; and a cutting guide attachedto the pivot member.
 2. The surgical instrument assembly of claim 1,further comprising a intramedullary rod defining an intramedullary axis,and wherein the angular adjustment mechanism is connected to theintramedullary rod, and the longitudinal axis of the adjustment memberis coaxial with the intramedullary axis.